1. Field of the Invention
The present invention relates to a method for making a seamless capsule comprising a shell material encapsulating a fill material by employing a concentrically aligned multiple nozzle system.
2. Description of the Prior Art
Seamless capsules containing a shell material encapsulating a fill material have been made for a variety of applications such as center-filled chewing gums, encapsulated medicines, foods, cosmetics, industrial chemicals, and the like. These seamless capsules are usually made by simultaneously extruding the shell material and the fill material through concentrically aligned nozzles such that the extruded shell material encapsulates the extruded fill material. Up to the present time, the mass ratio of the fill material to the shell material in the capsule is usually controlled by manipulating the volumetric flow rate of the shell material relative to that of the fill material through the nozzles. For example, Toshiyuki Suzuki, et al., "Process of Forming Seamless Capsules by Concentric Nozzle System," KONA Powder Science and Technology in Japan, No. 3 (1985) pp. 32-37 disclose a process for forming seamless capsules by experimenting with different flow rates for the shell and fill materials. However, controlling the mass ratio by varying the volumetric flow rates is often difficult and requires considerable experimentation of different flow rates for different shell and fill materials, thereby making the process inefficient and difficult to achieve steady state. In addition, adjusting flow rates to control mass ratio often requires the core material to move at a different flow rate than the shell material, thereby resulting in process instabilities and capsules that have leaky cores.
The present invention overcomes the drawbacks of the prior art by providing a novel method for preparing a seamless capsule by setting the fluid volumetric flux of the shell material equal to that of the fill material through the concentrically aligned nozzles. As a result, the mass ratio of the fill material to the shell material in the capsule can be controlled by merely varying the size of the orifice areas of the concentrically aligned nozzles without experimenting with the flow rates, thereby making the process efficient and easy to achieve steady state. The resultant capsules have excellent shell integrity and few leaky cores.